In the vast number of insole inserts designed and developed to mitigate podiatric problems, few embody physiological and kinesological aspects relating to locomotion and especially the problem of foot pronation. With few exceptions, the general conceptions relate to arch suport and shock absorption. Increased participation of the general population in athletic activity and primarily running has led to a notable increase in foot problems associated with pronation.
An abnormally pronated foot is one of the most common problems suffered by today's athletes, and in particular, by distance runners. While pronation may be caused by preexisting conditions, it may also be imposed upon a normal foot by overuse or injury during exercising. As is well known to those skilled in the art, a pronated foot disrupts the normal path of weight bearing and causes exaggerated internal rotation of the leg. This abnormal weight bearing causes functional changes in the foot, including, most commonly, a flattening of the longitudinal arch appearing on the plantar surface of the foot.
In order to better understand the concepts involved in locomotion, a description of the physiology and kinesiology of the foot is briefly reviewed. The foot is divisable into various regions. First, the lower surface of the foot is referred to as the plantar surface. The instep or interior side of the foot is termed medial while the outer side is the lateral. Concerning the bone structure and starting from the anterior (toes) to the posterior (heel), the several longitudinally extending bones are labeled, sequentially, the phalages, metatarsals, cuneiforms, naviculars, tali and finally the calcaneus (heel bone). The joints between these respective bones adopt the names of the two bones followed by articulation. For example, the joint between the metatarsal and phalanx of the big toe would be denominated the first metatarsal-phalanges articulation. Additional skeletal and muscle structures will be identified as applicable.
Turning now to a brief description of pronation, its general definition means "turning". As applied to the foot, it is a medical description of the turning of the foot relative to its medial longitudinal axis during locomotion. A certain amount of foot pronation is necessary. However, abnormal pronation often experienced during intense locomotion, principally during athletic activities where body weight on the heel, being multiplied by as many as four times, can result in a serious foot injury.
In the past, treatment of abnormally pronated foot conditions consisted of rest, physical treatment and rehabilitation. Physical treatments consisted of applying ice massages, cold whirpools, and muscle stimulation to help reduce inflammation and soreness which resulted from this condition. Further, administration of anti-inflammatory medications are used to mitigate swelling and soreness. Alternatively, some specialists have developed foam rubber arch supports covered with moleskin to help release some of the stress. Additionally, insertable arch supports are used which conform to the shape of the foot in a particular weight bearing position.
In keeping with the ancient bromide, "An ounce of prevention is worth a pound of cure", much effort has been dedicated to maximizing proper foot health. A veritable army of patents have issued for foot supports of various natures which contemplate and embody orthotic concepts. Some specifically consider abnormal pronation. Such devices have been around since the beginning of this century, as exemplified by U.S. Pat. No. 1,137,092 issued to C. Sharp in 1915. That patent includes a description of an insole constructed to resist "roll" of the foot. Greenberg in U.S. Pat. No. 2,008,207 addresses foot physiology in detail in the disclosure relating to an insole or shoe insert featuring a raised medial portion and a counter-balancing raised anterior lateral portion to prevent overstressing the lateral, fifth ray extending between the little toe and the heel.
More recent developments in this technical field are embodied in patent disclosures of Brown U.S. Pat. No. 4,510,700; Del Vecchio U.S. Pat. No. 4,084,333; Marsh U.S. Pat. No. 4,453,272; and Gudas U.S. Pat. No. 4,268,980. Referring briefly to each, Brown addresses a shoe sole insert formed of a closed-cell, foamed, plastic blank insert within a rigid cap. The cap is designed to provide controlled support for the heel to control pronation. Del Vecchio relates to a foot-supporting innersole having a plantar surface compatible configuration including a depression of parabolic contour for the heel and a corrugated anterior portion for receiving the toes. Marsh describes an orthotically-designed open sandal incorporating a structure which assists to prevent pronation while Gudas discloses a detorquing heel control insert of an elastomeric material having a Shore hardness of between 30-80 and an arcuate posterior ribbed portion to mitigate the effects of heel impact force on the foot.
Although the above-described devices and those others in this technical art field are not ineffective for their intended purposes, not one of the devices contemplates an insert which is designed to prevent abnormal pronation based strictly on the physics of locomotion and the biomechanical principles of pronation.